Silver complex diffusion transfer process

ABSTRACT

An improved silver complex diffusion transfer copy image is obtained when for purposes of better sensitivity and/or continuous-tone reproduction, a silver bromide or silver bromoiodide emulsion is utilized as the light-sensitive emulsion from which diffusion transfer takes place, by forming the diffusion transfer image in the presence of a quaternary phosphonium salt wherein three of the quaternary substituents are aryl groups and the fourth is an alkyl group. Known diffusion transfer additives, especially the tetrazoline-5 thiones and certain water soluble amines are preferably used together with the phosphonium salt.

United States Patent Vandeputte et a].

[ 1 Mar. 21, 1972 [541 SILVER COMPLEX DIFFUSION TRANSFER PROCESS [72]Inventors: Camille A. Vandeputte, Mortsel; Paul Desire Van Pee, Ede'gem,both of Belgium [52] US. Cl. ..96/29 R, 96/52, 96/58, 96/66 R [51] Int.Cl ..G03c 5/54 [58] Field of Search ..96/29, 52,58, 66R

[56] References Cited UNITED STATES PATENTS 2,238,632 4/1941 Dersch etal.... 96/109 2,271,622 2/1942 Carroll et al.... .96/104 3,017,2701/1962 Tregillus et a1. 96/58 X 3,161,506 12/1964 Becker ..96/33,314,789 4/1967 White et a1 ..96/52 X 3,431,108 3/1969 Willems et a1...96/52 X FOREIGN PATENTS OR APPLICATIONS 1,042,477 9/ 1966 GreatBritain ..96/29 1,052,022 12/1966 Great Britain ..96/29 1,054,253 l/1967Great Britain ..96/29 OTHER PUBLICATIONS Bylemans, Image TransferProcess," Progress in Photography, Vol. III, pps. 24- 37 1958.

Primary Examiner-William D. Martin Assistant Examiner-Harry J. GwinnellAttorney-William J. Daniel [57] ABSTRACT An improved silver complexdiffusion transfer copy image is obtained when for purposes of bettersensitivity and/or continuous-tone reproduction, a silver bromide orsilver bromoiodide emulsion is utilized as the light-sensitive emulsionfrom which diffusion transfer takes place, by forming the diffusiontransfer image in the presence of a quaternary phosphonium salt whereinthree of the quaternary substituents are aryl groups and the fourth isan alkyl group. Known diffusion transfer additives, especially thetetrazoline-S thiones and certain water soluble amines are preferablyused together with the phosphonium salt.

16 Claims, No Drawings SILVER COMPLEX DIFFUSION TRANSFER PROCESS Thepresent invention relates to a method of producing images according tothe silver complex diffusion transfer process.

The principle of the silver complex diffusion transfer process isgenerally known and comprises the image-wise exposure and development ofa light-sensitive silver halide emulsion layer, the complexation ofundeveloped silver halide in the unexposed areas of the emulsion layerand the diffusion of the complexed silver halide thus formed to a layeror surface where a substance or substances are present that promoteconversion of the said complexed silver halide to form a visible image.

In carrying out the silver complex diffusion transfer process mostlysilver chloride emulsions are used in that mostly the reproduction of aline original on an image-receiving material having a paper support isintended and no camera sensitivity is required. However, when a highsensitivity is required and/r continuous-tone reproductions have to bemade and/or a copy has to be produced on a usual transparent hydrophobicfilm support, silver bromide or silver bromo-iodide emulsions are used.

The substances normally applied for improving the image tone when silverchloride emulsion layers are used are not sufficiently effective whensilver bromide or silver bromo-iodide type emulsions are used.

It is an object of the present invention to provide compounds that in asilver complex diffusion transfer process wherein a silver bromide or asilver bromo-iodide emulsion is used, considerably improve the imagetone of the diffusion transfer image produced and have some furtheradvantageous effects detailedly described hereinafter.

According to the present invention these objects are accomplished bycarrying out the diffusion transfer process in the presence of a welldefined type of phosphonium salts. Thus the present invention relates toa method of producing images according to the silver complex diffusiontransfer process wherein the light-sensitive emulsion layer is a silverbromide or silver bromo-iodide emulsion layer, said process beingcharacterized by the fact that it is carried out in the presence of aphosphonium salt corresponding to the following formula:

wherein:

each of R R and R represents an aryl group, e.g., phenyl, chlorophenyl,bromophenyl, alkoxphenyl, tolyl, naphthyl, biphenylyl R represents analkyl group, e.g., methyl, cyanomethyl, carboxymethyl and estersthereof, ethyl, hydroxyethyl, heptyl, benzyl, chlorobenzyl, bromobenzyl,nitrobenzyl, and

X represents an acid radical.

The acid radical preferably is chloride, bromide, iodide, perchlorate,thiocyanate, benzenesulphonate, p-toluene sulphonate, or an alkylsulphate e.g., methylsulphate or ethylsulphate.

Examples of specific compounds according to the above formula that haveproved to be especially suitable for carrying out the method of thepresent invention are methyltriphenylphosphonium chloride,methyltriphenylphosphonium methylsulphate, ethyltriphenylphosphoniumiodide, (cyanomethyl)-triphenylphosphonium bromide,(carboxymethyl)-triphenylphosphonium chloride ethyl ester,benzyltriphenylphosphonium chloride, benzyltriphenylphosphonium bromide,benzyltriphenylphosphonium isothiocyanate, (2,5-dichlorobenzyl)-triphenylphosphonium chloride,(pnitrobenzyl)-triphenylphosphonium bromide,n-heptyltriphenylphosphonium bromide,(2-hydroxyethyl)-triphenylphosphonium chloride,(2-hydroxyethyl)-tri-ptolylphosphonium chloride,methyl-trinaphthylphosphonium methylsulphate,ethyl-tri(p-chlorophenyl)-phosphonium ethylsulphate,ethyl-tri(biphenylyl)-phosphonium sulphate. 7

Two or more phosphonium salts may be used together. The phosphoniumsalts are preferably dissolved in a minor amount of a suitablewater-miscible organic solvent, e.g., a lower alcohol or the methylether of ethylene glycol, whereupon this solution is added to thecoating composition of the layer in which the phosphonium salt has to beincorporated or to a processing liquid applied in carrying out thediffusion transfer image formation. t

The phosphonium salts for use in carrying out the method of the presentinvention favorably influence the tone of the diffusion transfer imageproduced in that they shift this tone to a warm black or bluish blacktone. Besides, the phosphonium salts influence the gradation ofcontinuous-tone diffusion transfer images: the sensitometric curve showsa steeper gradation in its toe. Finally, it has been observed that thephosphonium salts increase or decrease the maximum density of thediffusion transfer image dependent on the concentration in which theyare applied.

In carrying out the method of the present invention the phosphoniumsalts may be incorporated into the photographic material(s) used, i.e.,in the light-sensitive material, and/or in the image-receiving material,or occasionally in the multilayer material comprising both thelight-sensitive silver bromide or silver bromo-iodide emulsion layer andthe imagereceiving layer. In the material(s) used the phosphonium salthas to be present in (a) layer(s) in effective contact with theimage-receiving layer and/or in the image-receiving layer itself. By thewording effective contact is meant that at least an effective part ofthe phosphonium salt by diffusion reaches the image-receiving layer indue time, i.e., at the stage of the diffusion transfer image formation.

Generally, however, the phosphonium salts have proved to be the mosteffective when used in the processing liquid for carrying out thediffusion transfer image formation, i.e., an aqueous alkaline liquidthat may contain developing sub stances. The phosphonium salts can alsobe incorporated into another processing liquid applied in the productionof the diffusion transfer image, e.g., in a separate aqueous liquidmostly containing development nuclei. Of course the phosphonium saltscan also be present simultaneously in a processing liquid and in atleast one of the materials used.

In the materials used the phosphonium salt mostly is applied in aconcentration of 10 to 400 mg. per sq.m. of material, and in aprocessing liquid in a concentration of 10 to 500 mg. per liter.

The present invention also relates to photographic materials andprocessing liquids as described above and containing a phosphonium saltaccording to the above formula.

In carrying out the method of the present invention it is oftenadvantageous to use together with the phosphonium salt at least oneother compound whose favorable effect on the tone of the diffusiontransfer image is known. As especially suitable compounds of that kindmay be mentioned tetrazoline-S-thiones, e.g.,l-phenyl-2-tetrazoline-5-thione, and certain water-soluble amines. Theeffective amines include the primary aliphatic amines containing anunbranched carbon chain of from four to six carbon atoms, i.e., aminesof the n-butylto hexylamine series. Other amines which are effective arethe a, w-alkylene diarnines containing from three to 12 carbon atoms inthe alkylene chain, linking the amino groups, as in the series from a,m-propylene-diamine to a, wdodecylene-diamine. Also, one of the aminogroups of the diamine may be replaced by a hydroxyl group as in thealkanolamines. In addition, benzylamine and especially cyclohexylamineare most useful in carrying out the method of the invention. Thetetrazoline-S-thiones as well as the amines referred to above furtherdarken the tone of the diffusion transfer image.

The tetrazolihe-S-thiones are preferably incorporated into thelight-sensitive material, but can also be added to the processingliquid, to the image-receiving material and, if a ethylmultilayermaterial is used, to this material. If incorporated into the silverhalide emulsion layer, the tetrazoline-S-thione moreover exerts astabilizing effect on the light sensitive material. In the lattermaterial the tetrazoline-S-thione generally is present in aconcentration up to 5 mg. per sq.m.

Preferably, the amines are not incorporated into the material(s) but ina processing liquid, especially in the alkaline processing liquid forcarrying out the diffusion transfer image formation mostly in aconcentration of from 0.2 to g. per liter.

According to a preferred embodiment both a tetrazoline-S- thione and asuitable amine are used together with the phosphonium salt, thetetrazoline-S-thione mostly being incorporated into the silver halideemulsion layer, and the amine and the phosphonium salt in the alkalineprocessing liquid,

The method of the present invention may be carried out veryadvantageously with a so-called multilayer material comprising both alight-sensitive silver bromide or silver bromoiodide emulsion layer andan image-receiving layer containing a substance or substances (furtheron called development nuclei or shortly nuclei) for promoting theconversion of complexed silver halide so as to form a visible image, orto which such nuclei are added during processing. The light-sensitivesilver halide emulsion layer preferably is situated on top of theimage-receiving layer as described in German Pat. specification No.1,032,091, filed Apr. 18, 1957, by Kodak in the UK. Pat. specificationsNo, 746,948, filed Oct. 22, 1952, by Kodak and No. 1,006,292, filed Apr.30, 1962, by Gevaert Photo- Producten N.V., but it can also be comprisedbetween the support and the nuclei-containing layer as is known from theU.K. Pat. specifications No. 746,186, filed May 1, 1953, by Kodak andNo. 758,627, filed Dec. 6, 1954, by Agfa. On top of the silver halideemulsion layer the nuclei can be supplied at the processing stage inthat they are present in the aqueous alkaline processing liquid forcarrying out the diffusion transfer image formation as described, e.g.,in U.K. Pat. specifications No. 1,001,558, filed Apr. 13, 1962, and No.1,052,022, filed Aug. 2, 1963, both by Gevaert Photo-Producten N.V., orin another processing liquid to be applied before the wetting stage withthe alkaline processing liquid as is known, e.g., from the publishedDutch Pat. application No. 68,00432, filed Jan. 1 l, 1968, byGevaert-Agfa N.V. It is also within the scope of the present inventionto incorporate the phosphonium salt and/or some other substances, e.g.,a tetrazoline-S-thione and/or an amine (both types of compounds alreadyreferred to above), into another processing liquid than the alkalineprocessing liquid for carrying out the diffusion transfer imageformation, e.g., in a separate processing liquid supplying developmentnucleiv For the embodiment according to which the diffusion transferimage is produced on top of the silver halide emulsion layer, thediffusion transfer image may be physically transferred to a receivingmaterial, as it is the case according to the method of U.K. Pat.specifications NO. 746,186, filed May 1, 1953, by Kodak No. 758,627,filed Dec. 6,1954, by Agfa, No. 1,001,558, filed Apr. 13,1962, and No.1,052,022, filed Aug. 2, 1963, both by Gevaert Photo-Producten N.V.referred to above. For more particulars on the specific embodimentsaccording to which the diffusion transfer image is produced on top ofthe silver halide emulsion layer, reference is made to the patentspecifications cited above.

According to the preferred embodiment, according to which theimage-receiving layer is situated between the silver halide emulsionlayer and the support of the multilayer material the silver halideemulsion layer mostly is removed after the diffusion transfer image hasbeen produced. In carrying out the method of the present invention thissupport preferably is a transparent hydrophobic synthetic film supportsuch as a support of a cellulose ester, e.g., cellulose triacetate, orof a polyester, e.g., polyethylene terephthalate. The diffusion transfercopy obtained on such transparent support is very suited to be used asan intermediate in all sorts of reproduction techniques.

1n the case the support of the multilayer material is a transparentsupport and the negative image produced in the outer silver halideemulsion layer is sufficiently screened from the eye on examining thediffusion transfer image produced in the underlying image-receivinglayer through the support, as is the case according to the UK. Pat.specification No. 746,948, filed Oct. 22, 1952, by Kodak referred toabove, the silver halide emulsion layer is not removed after thediffusion transfer image has been produced.

Of course, the way in which the method of the present invention iscarried out may be the most usual one, viz with the use of a separatelight-sensitive material comprising a lightsensitive silver bromide orsilver bromo-iodide emulsion layer, and a separate image-receivingmaterial comprising development nuclei, incorporated therein at thepreparation stage, which is the most conventional embodiment, or appliedat the processing stage by means or the aqueous alkaline processingliquid, or by a preliminary treatment with a liquid compositioncontaining development nuclei. The development nuclei may also becontained in a pod and at the processing stage will be spread over thelayer wherein or whereon the diffusion transfer image will be produced.

Summarizing one can say that the method of the present in vention alwayscomprises the steps of image-wise exposing a light-sensitive silverbromide or silver bromo-iodide emulsion layer, wetting thelight-sensitive layer with an aqueous alkaline processing liquid in thepresence of a developing substance whereby an image is developed in theexposed areas of the light-sensitive layer, and keeping thelight-sensitive layer, in the presence of a complexing agent for silverhalide, in effective contact with an image-receiving layer containingdevelopment nuclei, whereby complexed silver halide diffuses from theunexposed and undeveloped areas of the light-sensitive layer to thereceiving layer where a diffusion transfer image is formed. By thewording effective contact" is understood such a contact that thediffusion of complexed silver halide can take place.

More particulars on the general composition of the materials used, thevarious ingredients to be incorporated therein, the techniques for theproduction of the diffusion transfer image, suitable apparatus forcarrying out the various processing steps and further general dataconcerning the image formation according to the silver complex diffusionprocess can be found in the patent specifications referred to above andhereinafter and in Progress in Photography" Vol. I, 1940-1950, pages76-77 and vol. 11, 1951-1954, pages 1567; vol. 111, 1955-1958, pages24-36 and the patent literature cited therein.

As essential ingredients in the diffusion transfer process may bementioned developing substances, preferably hydroquinone and a3-pyrazolidinone developing compound, e.g., l-phenyl-3-pyrazolidinoneand/or 1-phenyl-4-methyl -3- pyrazolidinone, a complexing agent forsilver halide and an alkaline substance. Further ingredients oftenapplied are preservatives for developing substances, stabilizers,anti-yellowing agents, toning agents and anti-silver sludge agents,hardeners including latent hardening agents, softening agents, coatingaids, etc.

With respect to the developing substances it has to be mentioned thatsometimes they are omitted at least partially from the aqueous alkalineprocessing liquid and that they are incorporated into the material(s)used, whereby the alkaline processing liquid can be restricted to a mereaqueous alkaline liquid, which is substantially free from any developingsubstance. Such a processing liquid is called an activator. For moreparticulars on this matter reference is made to UK. Pat specificationsNo. 1,012,476, filed Dec. 18, 1961, No. 1,042,477, filed June 17, 1963,No. 1,054,253, filed Aug, 6, 1963, No. 1,057,273, filed Feb. 3, 1964,all by Gevaert Photoproducten N.V., and Nos. 1,086,510, 1,093,177, bothfiled Dec. 16, 1964, by Gevaert-Agfa NV.

The following examples illustrate the method and the materials accordingto the present invention.

Example 1 A suspension of the following composition was prepared:

water 950 ccs. gelatin 30 g. sodium alginate g. 01% aqueous suspensionof colloidal silver sulphide 5 ccs. aqueous solution of formaldehyde 2ccs.

sodium salt of oleyl methyl tauride 1 cc.

From this suspension an image-receiving layer was coated onto a subbedtransparent film support in such a way that the weight of the driedlayer amounted to 2.5 g./sq.m. The transparent film support was abiaxially stretched polyethylene terephthalate sheet of 120 g./sq.m. andthe subbing layer consisted of a polyethylene isophthalate layer appliedto the sup-,

port and a mixed gelatin cellulose nitrate layer on top thereof.

To the image-receiving layer a further layer was applied, starting fromthe following solution:

hydroxyethyl starch having a substitution degree of0.27

of hydroxyethyl groups 10 g. water I000 ccs. 5% solution of the sodiumsalt of dioctyl sulfosuccinic acid in water/ethanol 50/50 2 ccs.

This solution was coated in such a say that l I. covered 40 sq.m. ofpaper support.

After drying an orthochromatic and contrasty silver bromide emulsionwith camera sensitivity and per kg. containing 13 g. of silver bromideand 36 g. of gelatin was applied thereto in such a way that the finallyobtained emulsion layer contained 2.4 g. of silver bromide per sq.m.

After image-wise exposure the thus prepared multilayer material wasprocessed in an alkaline developing liquid of the following compositiontrisodium salt of ethylenediamine tetruacetic acid 1.5 g. sodiumsulphite 75 g. hydmquinone 20 g. l-phenyl-Lpyrazolidinone l g. potassiumbromide 2 g. sodium thiosulphute 20 g. sodium hydroxide l2 g. orthoboricacid 2 g. solution of 0.4 g. of(2-hydroxyethyl)- triphenylphosphoniumchloride in 30 ccs. of

munomethyl ether of ethylene glycol l2.57r aqueous solution of saponine5 ccs. polyelhyleneglycol (moLweight ca 200) 50 mg. water up to I000ccs.

After some 2 to 3 minutes the multilayer material was brought intorinsing water at room temperature and after some 20 to 30 seconds thesilver halide emulsion layer detached as a coherent membrane withoutmechanical help. A positive transparency having an excellent blackimage-tone was obtained. This transparency is very suited as anintermediate in diazotype printing of in the production of offsetprinting plates.

Example 2 The method of Example 1 was repeated with the differencehowever, that 1-phenyl-2-tetrazoline-5-thione was added to the silverhalide emulsion in such an amount that after coating 2 mg. was presentper sq.m. of the multilayer material. Besides, the alkaline developingliquid was replaced by the following one:

4071 aqueous solution of potassium hydroxide 75 ccs. 40% aqueoussolution of sodium hydroxide l4 ccs. trisodium salt of ethylenediaminetetraacetic acid 3 g. anhydrous sodium sulphite 110 g. anhydrouspotassium metabisulphite 7.5 g hydroquinone 40 g. potassium bromide 4 g.l-phenyl-S-pyrazolidinone 2 g. anhydrous sodium thiosulphate 30 g.cyclohexylumine L75 ccs.

solution of 0.4 g. of (Z-hydroxyethyl) triphenylphosphonium chloride in30 cos. of monomethyl ether of ethylene glycol 12.571 aqueous solutionof saponine 5 ccs. sodium salt ofdioctylsulpho-succinic acid 50 mg.water up to 2000 ccs.

A positive transparency having an excellent black image tone wasobtained. This transparency is very suited as an intermediate in allkind of reproduction techniques.

Example 3 An image-receiving material was prepared by applying animage-receiving layer as described in Example 1 to a subbed polyethyleneterephthalate support as described in that some Example 1.

A light-sensitive material was prepared by applying a silver bromideemulsion layer as described in Example l to a paper support and bycoating a hydroxyethyl starch layer as described in Example 1 on topthereof.

After image-wise exposure of the light-sensitive material it wasconducted together with the image-receiving material through thealkaline developing liquid described in Example 2. Then thelight-sensitive and the image-receiving material were pressed againsteach other and after some 3 minutes separated again.

The positive diffusion transfer copy thus obtained showed an excellentblack image tone, and is very suited as an intermediate transparency inall kind of reproduction techniques.

What we claim is:

1. In a method of producing black and white silver metal imagesaccording to the silver complex diffusion transfer process whichcomprises image-wise exposing a light-sensitive silver halide emulsionlayer and treating the light-sensitive layer with an aqueous alkalineprocessing liquid in the presence of a silver halide developingsubstance and a silver halide complexing agent while in contact with animagereceiving layer containing development nuclei, whereby theunexposed and undeveloped silver halide in said emulsion layer aftercomplexing with said complexing agent diffuses to said image-receivinglayer and is precipitated thereon by said nuclei as a black and whitesilver metal image, the improvement which comprises using aslight-sensitive silver halide emulsion layer a light-sensitive silverbromide or silver bromoiodide emulsion layer and treating the said layerwith the said aqueous alkaline processing liquid in the presence of aphosphonium salt corresponding to the formula:

wherein:

each of R,, R and R is an aryl group,

R is an alkyl group having from one to seven carbon atoms therein, and

X is an acid radical.

2. Method according to claim 1, wherein the acid radical is selectedfrom the group consisting of chloride, bromide, iodide, perchlorate,thiocyanate, benzenesulphonate, ptoluene sulphonate, and alkyl sulphate.

3. Method according to claim 1, wherein the light-sensitive emulsionlayer and image-receiving layer form part of a multilayer material inorder comprising a support, said imagereceiving layer containingdevelopment nuclei and the lightsensitive emulsion layer.

4. The method according to claim 3 wherein said support is a transparenthydrophobic film.

5. Method according to claim 1, wherein the phosphonium salt is presentin the aqueous alkaline processing liquid for carrying out the diffusiontransfer image formation.

6. Method according to claim 5, wherein the phosphonium salt is presentin an amount of 10 to 500 mg. per liter of the aqueous alkalineprocessing liquid.

7. Method according to claim 5, wherein the phosphonium salt is a(2-hyclroxyethyl)-triphenylphosphonium halide.

8. Method according to claim 7, wherein the light-sensitive emulsionlayer comprises l-phenyl-2-tetrazoline-5-thione and the aqueous alkalineprocessing liquid for carrying out the diffusion transfer imageformation contains cyclohexylamine.

9. Method according to claim 1, wherein the diffusion transfer imageformation is carried out in the presence of an additional compound,which favorably influences the image tone of the diffusion transferimage.

10. Method according to claim 9, wherein the said compound is atetrazoline-S-thione.

11. Method according to claim 10, wherein the tetrazoline- S-thione ispresent in the light-sensitive silver halide emulsion layer.

12. Method according to claim 11, wherein the tetrazoline- 5-thione isl-phenyl-2-tetrazoline-5-thione.

13. Method according to claim 9, wherein the said compound is awater-soluble amine.

14. Method according to claim 13, wherein the water-soluble amine ispresent in the aqueous alkaline processing liquid for carrying out thediffusion transfer image formation.

15. Method according to claim 14, wherein the water-soluble amine ispresent in an amount of 0.2 to 10 g. per liter of the aqueous alkalineprocessing liquid.

16. Method according to claim 14, wherein the water-soluble amine iscyclohexylamine.

2. Method according to claim 1, wherein the acid radical is selected from the group consisting of chloride, bromide, iodide, perchlorate, thiocyanate, benzenesulphonate, p-toluene sulphonate, and alkyl sulphate.
 3. Method according to claim 1, wherein the light-sensitive emulsion layer and image-receiving layer form part of a multilayer material in order comprising a support, said image-receiving layer containing development nuclei and the light-sensitive emulsion layer.
 4. The method according to claim 3 wherein said support is a transparent hydrophobic film.
 5. Method according to claim 1, wherein the phosphonium salt is present in the aqueous alkaline processing liquid for carrying out the diffusion transfer image formation.
 6. Method according to claim 5, wherein the phosphonium salt is present in an amount of 10 to 500 mg. per liter of the aqueous alkaline processing liquid.
 7. Method according to claim 5, wherein the phosphonium salt is a (2-hydroxyethyl)-triphenylphosphonium halide.
 8. Method according to claim 7, wherein the light-sensitive emulsion layer comprises 1-phenyl-2-tetrazoline-5-thione and the aqueous alkaline processing liquid for carrying out the diffusion transfer image formation contains cyclohexylamine.
 9. Method according to claim 1, wherein the diffusion transfer image formation is carried out in the presence of an additional compound, which favorably influences the image tone of the diffusion transfer image.
 10. Method according to claim 9, wherein the said compound is a tetrazoline-5-thione.
 11. Method according to claim 10, wherein the tetrazoline-5-thione is present in the light-sensitive silver halide emulsion layer.
 12. Method according to claim 11, wherein the tetrazoline-5-thione is 1-phenyl-2-tetrazoline-5-thione.
 13. Method according to claim 9, wherein the said compound is a water-soluble amine.
 14. Method according to claim 13, wherein the water-soluble amine is present in the aqueous alkaline processing liquid for carrying out the diffusion transfer image formation.
 15. Method according to claim 14, wherein the water-soluble amine is present in an amount of 0.2 to 10 g. per liter of the aqueous alkaline processing liquid.
 16. Method according to claim 14, wherein the water-soluble amine is cyclohexylamine. 